What is spinal cord auto regulation?

Spinal Cord Autoregulation

Spinal cord autoregulation is a critical physiological mechanism that maintains constant blood flow to the spinal cord despite fluctuations in systemic blood pressure, primarily through arteriole diameter changes that can dramatically alter blood flow according to Poiseuille's law. 1

Mechanism of Spinal Cord Autoregulation

• Autoregulation occurs through changes in arteriole diameter, where resistance is reduced by the fourth power of increases in vessel radius
• This allows the spinal cord to maintain constant blood flow despite fluctuations in systemic blood pressure
• The autoregulatory range for spinal cord blood flow mirrors that of the brain, functioning between 60 to 120 mmHg mean arterial pressure 2
• Within this autoregulatory range, spinal cord blood flow averages approximately 61.1 ± 3.6 ml/100g/min, which is comparable to cerebral blood flow (59.2 ± 3.2 ml/100g/min) 2

Regional Autoregulation

• Autoregulation occurs throughout different regions of the spinal cord, including cervical, thoracic, and lumbar segments 2
• Similar to the brain, the spinal cord demonstrates regional autoregulatory capabilities that help maintain adequate perfusion to all segments

Factors Affecting Autoregulation

• Respiratory factors: Hypocapnia (low CO₂) can alter blood flow by widening the plateau on the autoregulatory curve 1
• Anesthetics: Barbiturates and other anesthetic agents may affect intraspinal cord compliance and autoregulation 2
• Spinal cord injury: High-level spinal cord injury (above T6) significantly impacts autoregulatory mechanisms 3

Autoregulation After Spinal Cord Injury

• While static cerebral autoregulation appears to be maintained after high-level SCI, dynamic cerebral autoregulation, cerebrovascular reactivity, and neurovascular coupling are markedly altered 3
• Disruption of connections between higher brain centers and the spinal cord leads to autonomic dysfunctions that affect cardiovascular control 4
• After high cervical SCI, parasympathetic (vagal) control remains intact, while spinal sympathetic circuits lose their tonic supraspinal autonomic control 5
• These changes can lead to orthostatic hypotension and autonomic dysreflexia, which challenge the autoregulatory capacity of the spinal cord 3

Monitoring and Assessment

• Monitoring and assessment of autoregulation may be useful in targeting perfusion management goals in acute spinal cord injury 1
• Continuous bedside monitoring of autoregulation is feasible using various techniques, including:
  • Pressure reactivity index (PRx)
  • Transcranial Doppler ultrasound
  • Near-infrared spectroscopy (NIRS) 1
• These methods can help determine optimal perfusion pressure targets and aid in prognostication 1

Clinical Implications

• Failure of autoregulation is associated with worse outcomes in various acute neurological diseases 1
• Understanding spinal cord autoregulation is essential for managing patients with spinal cord injury to prevent secondary injury
• Maintaining appropriate blood pressure within the autoregulatory range (60-120 mmHg) is critical for preserving spinal cord perfusion 2
• Inflammatory responses after spinal cord injury may further compromise autoregulatory mechanisms 6

Spinal cord autoregulation represents a critical physiological mechanism that parallels cerebral autoregulation but has distinct characteristics based on the unique anatomy and vascular supply of the spinal cord. Proper understanding of these mechanisms is essential for optimizing patient outcomes after spinal cord injury.